You Yawn Because You Need Oxygen? – No, says researchers.

State University of New York researchers questioned the old myth that a person yawns because of a need to increase oxygen levels.
The researchers concluded that people yawn to allow air in to cool their brains.
In their experiment, the researchers found that those who watched others yawn had the urge to yawn as well. However, those who held an ice pack to their forehead or those who breathed with their noses did not have the urge to yawn.